1. Field of the Invention
The present invention relates to a medical analysis apparatus of the type having a predetermined number of electrodes for placement at specific locations on a patient in order to pick up electrical signals from the patient, and a control unit for determining, on the basis of a predetermined number of input signals generated from the recorded electrical signals, whether any of the electrodes is incorrectly attached to the patient.
2. Description of the Prior Art
As used herein, an "incorrectly attached" electrode means an electrode which has been placed in the wrong location and/or is not in good electrical contact with the patient. "Patient" refers to any living creature, but henceforth only human patients will be exemplified.
One such analysis apparatus of the above type is the Mingograf Model 740, Siemens-Elema AB, Sweden. This known analysis apparatus is an ECG analysis apparatus and utilizes ten electrodes which are applied to the patient at specific locations. One electrode is applied to each arm and leg and the six remaining electrodes are applied to the chest. The three electrodes applied to the left arm, right arm and left leg, respectively, can be used for bipolar sensing of the heart's electrical signals. The following combinations are then possible: sensing between the right and left arm electrodes (designated lead I), sensing between the right arm and left leg electrodes (designated lead II) and between the left arm and left leg electrodes (designated lead III). These three electrodes can also be combined in pairs via resistors to form an indifferent electrode for the third electrode. Accordingly, the electrodes for the left arm and left leg can be combined to form an indifferent electrode for the electrode on the right arm (designated lead aVR), the electrodes for the right arm and left leg can be combined to form an indifferent electrode for the electrode on the left arm (designated lead aVL) and the electrodes for the right arm and the left arm can be combined to form an indifferent electrode for the electrode on the left leg (designated aVF). These three extremity electrodes can therefore be utilized for sensing in up to six measurement channels (leads I, II, III, aVR, aVL and aVF).
The six chest electrodes are designated V1-V6 and are applied to the chest in a specific sequence. The electrode on the right leg is grounded.
The ECG analysis apparatus further includes a control unit for determining whether the electrodes for the right and left arms have been correctly applied to the patient, i.e., whether the electrode for the right arm really has been placed on the right arm and whether the electrode for the left arm really has been placed on the left arm, and not the reverse. The control unit is programmed with a specific analysis program for performing this check. The analysis program uses certain signal parameters as input signals, derived from the measurement signals picked up by the electrodes. If the analysis program determines that an electrode placement mistake has occurred, an error message is generated which reports the suspicion of erroneous electrode application.
Discovering erroneously applied electrodes is important, since proceeding to obtain measurement signals with incorrectly placed electrodes could cause a wrong diagnosis to be made. This applies to, e.g., modern ECG analysis apparatuses equipped with different analysis programs for evaluating recorded measurement signals. The measurement signals must be recorded in the correct manner for these programs to work properly.
Detecting erroneously applied electrodes, e.g. the above left-to-right reversal of electrodes, from the recorded ECG tracks can be difficult. In principle, this reversal means that measurement signals for leads II and III and for leads aVL and aVR are reversed and the signal on lead I is simultaneously inverted. The wide variation is signal appearance found in correctly recorded ECGs, however, means that not even highly experienced physicians can easily identify certain erroneously recorded ECGs.
Incorrectly attached electrodes might appear to be a problem which can be solved with careful routines for staff to be followed when applying the electrodes to the patient. It should be remembered, however, that an estimated 300 million ECG recordings are made each year world-wide. Even if the percentage of incorrectly attached electrodes is very small, a large number of ECG recordings could still be made with incorrectly attached electrodes. Further, incorrect attachment does not necessarily entail application of one or several electrodes to the wrong site. Correctly located electrodes whose electrical contact with skin is poor may also be involved. Poor electrical contact could result in the electrode's failure to record information important to the diagnosis. An incorrect diagnosis could lead to incorrect treatment, no treatment etc. Most state of the art computerized ECG analysis apparatuses thus incorporate some analysis program, as noted above, for identifying electrode reversal on the right and left arms.
The known analysis programs, however, are only able, in principle, to identify reversal of electrodes on the right and left arm. Other erroneous connections, such as reversal of the electrodes on the left arm and left leg, are much harder to detect, and no analysis program has been devised for detecting them.
One of these analysis programs, which is implemented in the above Mingograf Model 740, is known under the designation GRI and is described in "Comprehensive Electrocardiography, Theory and Practice in Health and Disease", Volume 3, Oxford, Pergamon Press Inc., 1989, page 1530.
Another of these analysis programs is described in the "Physician's Guide to Marquette Electronics Resting ECG Analysis", Dec. 88 000-90160-010, USA, page 53, and is implemented in equipment supplied by Marquette Electronics Inc.
Both of these analysis programs have relatively good specificity, i.e. they seldom supply an error indication when the electrodes have been correctly applied. These known analysis programs, however, have a sensitivity which is less reliable, i.e., they do not invariably supply an error indication when there is a genuine reversal of left and right arm electrodes. The sensitivity of these analysis systems is especially reduced when the ECG measurement signal lacks P waves. Examinations of a large number of ECG recordings has shown that sensitivity can drop to 30 to 40% for the two methods when the P wave is absent. In other words, the analysis methods only discover 30 to 40% of erroneous connection of electrodes on the right and left arms.